From time to time, crypto algorithms are deprecated for use in SSH. Absolute discourages use of deprecated algorithms are MAY in the future remove them. For maximum compatibility with older servers though, Absolute usually retains their functionality but notifies you that they’re being used. That notification for example may have brought you to THIS PAGE!
Newer servers often disable or remove deprecated algorithms altogether in favor of newer more secure algorithms. Older servers that need them may become inaccessible if the client functionality is removed entirely. If your server connection used a deprecated algorithm, you may want to consider updating your server!
In other cases, older algorithms fall out of favor, though not specifically deprecated. In each algorithm category, there is an algorithm list in order of preference. At connection time, the client and server will choose the FIRST compatible algorithm that both the client and server support. If the client and server have no algorithm in common, the connection fails. For the list of all supported algorithms and their current status, see SUPPORTED ALGORITHMS
DEFINITIONS:
Supported Algorithms: All algorithms supported in AbsoluteTelnet/ssh code. NEW algorithms can only be added in newer versions of the software
Deprecated Algorithms: Algorithms formally or informally discouraged from use, either by documented standard or general consensus. Only new versions of the software can move algorithms into this category.
Disabled Algorithms: Algorithms that won’t be used during connection. Initially, deprecated algorithms are also disabled, but as a user option, you can control which are disabled or enabled. As of Version 12.17, Absolute will recommend re-enabling a disabled algorithm but only when absolutely necessary for backward compatibility to older servers.
Compatible Algorithms: Decided at connection time, the client and server decide which algorithms will be used. If a compatible set can’t be found, the connection terminates.